The majority of primary brain tumors result in high morbidity and very poor survival. Brain tumors are now unfortunately the leading cause of cancer-related death in children. Medulloblastoma is the most common malignant pediatric brain tumor resulting in the death of nearly one-third of afflicted children despite very aggressive therapies that include surgical resection, whole brain and spine radiation therapy, and systemic chemotherapy. Furthermore, the vast majority of surviving children have poor outcomes and significant neurocognitive deficits due to the toxicity of these therapies. A major barrier to improving outcomes for primary brain tumor patients is the relative ineffective delivery of therapeutic agents across the blood-brain barrier (BBB) specifically to brain tumor cells while sparing normal surrounding brain tissue. Heretofore, researchers have found few mechanisms to target therapies specifically to primary brain tumors, to avoid systemic toxicities. We seek to address this problem to improve drug therapeutic indices by proposing a strategy to target therapies specifically to brain tumor vasculature utilizing a novel nanoparticle- based drug delivery system that has high affinity to P-selectin on endothelial cells within tumors. Our preliminary studies show selective nanoparticle extravasation and targeting to tumors across the blood-brain barrier in a novel autochthonous GEM medulloblastoma model. Our team proposes a strategy to localize both conventional and precision drugs to brain tumor tissue by targeting therapies to P-selectin on tumor vasculature. We will employ a physiologically and genetically-relevant mouse model of Sonic hedgehog-driven medulloblastoma to identify synergy with radiation therapy in enhancing tumor-selective nanoparticle drug delivery, and will pursue the following specific aims: 1) To evaluate the P-selectin-mediated targeting, role of radiation, and mechanism of extravasation across the blood-brain barrier in medulloblastoma, 2) To assess the efficacy and toxicity of P-selectin-targeted chemotherapy/SHH pathway inhibition in Sonic hedgehog-driven medulloblastoma, and 3) To assess the effects of focal radiation therapy of primary medulloblastoma tumors on P-selectin and nanoparticle drug delivery to distant leptomeningeal brain tumor metastases within the central nervous system in vivo. We will utilize biochemical and imaging methods including intravital multiphoton microscopy, confocal immunofluorescence and immuno-EM, micro-CT for bone analysis, pharmacokinetic and biodistribution measurements, and molecular biology approaches to assess nanoparticle delivery mechanisms, treatment efficacy, and toxicity. Our primary endpoint is to identify tumor-selective strategies that synergize with current standard of care therapies for medulloblastoma. Should our results prove favorable, we envision clinical applicability to patients with medulloblastoma and other primary brain tumors as well as neurological diseases that have been shown to have endothelial inflammation including multiple sclerosis and stroke.